Process for the hydrogenation of benzene



United States Patent M 3,484,367 PROCESS FOR THE HYDROGENATION 0FBENZENE John Winsor, Farnborough, England, assignor to The BritishPetroleum Company Limited, London, England, a corporation of England NoDrawing. Filed July 1, 1966, Ser. No. 562,124 Claims priority,application Great Britain, July 7, 1965, 28,768/ 65 Int. Cl. Cg 13/02U.S. 'Cl. 208-244 11 Claims ABSTRACT OF THE DISCLOSURE This inventionrelates to a process for the desulphurisation of aromatic feedstocks.

Fractions consisting of or containing aromatic hydrocarbons may beobtained from petroleum hydrocarbon feedstocks or by the destructivedistillation of coal. Such fractions are frequently contaminated withsulphur in a number of combined forms, and whether the fraction is to beused as such or it to be further processed it is usually necessary toremove this sulphur. This course is particularly necessary when thefraction is to undergo catalytic conversion over a sulphur-sensitivecatalyst. An important case where desulphurisation of an aromaticmaterial is necessary is that in which benzene is obtained, either froma petroleum feedstock by distillation and extraction procedures, or fromcoal, and then is hydrogenated over a nickel-containing catalyst to givecyclohexane. One of the major uses of cyclohexane is as an intermediatein the manufacture of nylon, and for this requirement a high level ofpurity is required. Nickel catalysts are used because they have goodactivity at low temperatures and because they are cheap, but they areextremely sensitive to sulphur-containing materials, and especially tothiophenic sulphur. This form of combined sulphur is one which is not aseasily removed by conventional hydrocatalytic desulphurisationprocedures as is, for example, mercaptan-type sulphur, and since thepresence of such sulphur in a hydrogenation feedstock would, in additionto deactivation of the catalyst and the effect this would have on theconversion efficiency, also adversely affect the hydrogenated material,it is clear that means must be found to remove or reduce the amount ofsulphur present before the feedstock is hydrogenated or is otherwiseused.

We have found that aromatic materials may be desulphurised over asupported nickel catalyst in such a way that the catalyst has a longlife and operating conditions are mild. The technique is particularlysuitable for removal of thiophenic sulphur, but since this is the mostdiflicult of all types of combined sulphur to remove, it will alsoremove other forms of sulphur. If desired, however, and if the feedstockcontains a large amount of sulphur, a preliminary catalytichydro-desulphurisation step may be employed. Hydrogen sulphide, ifpresent, may also be removed in known manner. Such materials, althoughremovable by the desulphurisation technique to be disclosed, wouldshorten the catalyst life unnecessarily unless removed previously. Thepresent technique can 3,484,367 Patented Dec. 16, 1969 ggtanomicallyremove up to 10 p.p.m. sulphur at up to We have found that for asupported nickel catalyst there is a threshold temperature. Above thistemperature the catalyst acts as a conventional hydrogenation catalystin the presence of hydrogen, but below it hydrogenation occurs only to alimited extent. Below the threshold temperature, however, the supportednickel material is capable of absorbing sulphur. The thresholdtemperature is comparatively low when the supported nickel material isfresh, but as it absorbs sulphur, and thereby becomes sulphided, thethreshold temperature increases. The sulphur capacity of the supportednickel increases with increasing temperature, so that by progressivelyincreasing the operating temperature so that this is just below thethreshold temperature the full capacity of the supported nickel may beused. The absorption effect is believed to be a massive effect, i.e. itis not merely a surface phenomenon, and the limit of sulphur capacityoccurs when the nickel is sulphided in depth. In terms of thesulphurznickel atomic ratio the capacity of a nickel on sepiolitematerial is 0.06:1 at C., 0.26:1 at 200 (1., and 0.46:1 at 250 C. Theultimate sulphur capacity at much higher temperatures may be as high as1:1. In practice all hydrogenation activity is lost at an averagesulphurznickel atomic ratio of about 0.1:1.

For convenience the term supported nickel catalyst has been used,although the effect is not catalytic in the accepted sense of the term.A small amount of hydrogen should be present, however, because it hasbeen found that in its absence a slow deactivation of the catalystsurface occurs. This is not due directly to the presence of sulphur, butit is thought that when ring type sulphur (i.e. thiophenic sulphur) isabsorbed, ring splitting occurs with combination of the sulphur with thenickel surface, leaving an unsaturated hydrocarbon fragment. It ispostulated that polymerisation of these unsaturated fragments takesplace and that consequently the nickel surface becomes blocked. Thepresence of as little as 3.7 X 10 litres of hydrogen (at NTP) per litreof feedstock when desulphurising a benzene feedstock containing 20p.p.m. thiophenic sulphur is sufficient to prevent this. The process isnot one of catalytic hydro-desulphurisation since hydrogen sulphide doesnot appear at the reactor outlet.

In accordance with the foregoing the invention consists in a process forthe desulphurisation of an aromatic feedstock which comprises contactingthe feedstock in the presence of hydrogen, with a supported nickelcatalyst at a temperature and pressure at which the catalyst hasdesulphurisation activity, but below that at which it has substantialhydrogenation activity, and progressively increasing the temperature,and, if desired, increasing the pres sure, as the catalyst takes upsulphur, the conditions of operation being such that no substantialamount of hydrogen sulphide is produced in the process.

The term aromatic feedstock includes feedstocks containing a majorproportion of aromatic hydrocarbons, the remainder of the feedstockbeing not such as to de-activate the catalyst surface or to besubstantially hydrogenated under the reaction conditions, and whollyaromatic fractions or individual aromatic hydrocarbons or mixtures ofsuch hydrocarbons not obtainable by distillation. The term aromatichydrocarbons includes substituted aromatic hydrocarbons in which thesubstituent group or nickel supported on a natural or synthetic support,such as, for example, a refractory oxide of Groups II to V of thePeriodic Table, or kieselguhr, pumice, or sepiolite. Sepiolite is thepreferred support. It is a commercially available clay mineral whichoccurs naturally, and may also be prepared synthetically. British PatentNo. 899,652 discloses and claims catalysts comprising nickel supportedon a base consisting essentially of sepiolite, and high surface area(and hence high activity) and high selectivity materials prepared andactivated according to the disclosures of this patent are the preferredcatalysts for use in the present process. Preferred catalysts containfrom 1 to 50% nickel (expressed as elemental nickel), and moreparticularly from 5 to 25% wt.

The hydrogen used in the present process may be commercially pure, or itmay be used as a mixture with one or more substantially sulphur-freereaction-inert constituents. A suitable mixed gas would be that obtainedfrom a steam reformer, containing 95% hydrogen, the remainder of the gasbeing methane. Gases containing hydrocarbons having two or more carbonsper molecule may be used, provided that reaction conditions arecarefully controlled to avoid cracking, which in the presence of thenickel catalyst might lead to an exothermic reaction and a temperaturerunaway. Preferably when inert constituents are present the hydrogencontent of the mixed gas should be at least 50 mole percent and moreparticularly from 70 to 99 mole percent.

Suitable operating conditions for the desulphurisation of an aromaticfeedstock according to the invention may be selected from the following:

Temperature, C.-Progressively increased within the range 50 to 290 C.(122 to 554 F.) corresponding to a sulphurznickel atomic ratio of0.035z1 to 0.053zl. The preferred range is 75 to 250 C. (167 to 482 F.)corresponding to a sulphurznickel atomic ratio of 00.51: 1 to 0.46:1.

Pressure, p.s.i.g.-- to 2000, preferably 0 to 50 up to a sulphurznickelatomic ratio of 0.1:1, and then 502000.

Space velocity, v./v./hr.0.05 to 10.0 (preferably 0.2 to

Inlet hydrogen: hydrocarbon ratio on total feed, molar- 0.01 to :1(preferably 0.05 to 0.2:1).

In actual operation the reaction pressure may be increased stepwise,since it has been found that this increases the extent ofdesulphurisation at a given temperature. However, it also increases theextent of hydrogenation taking place at that temperature, and thereforelowers the threshold temperature. The process is carried out, when usinga fresh catalyst, by passing the feedstock over the catalyst at atemperature and pressure close to the lower limits of the ranges givenabove, at which it is known that hydrogenation will not occur to anextent sufficient to cause an unacceptable temperature rise. The sulphurcontent of the effluent from the process, and its naphthene content, aresurveyed and when the sulphur content increases to above a set level thetemperature, and, if desired, the pressure, are increased to such anextent that the set value is attained. If the naphthene contentincreases above the desired level, the temperature and, optionally,pressure, need to be reduced. The actual values of temperature andpressure are, accordingly compromise values.

Although operation below the threshold temperature means that sulphurabsorption is by far the main reaction occurring, some hydrogenation ofthe feedstock does occur, and this may be an exothermic reaction. Thusin the case of benzene hydrogenations, a temperature rise of 28 F. mayoccur for each one percent conversion to cyclohexane at 440 F. Thedegree of hydrogenation that occurs in the present desulphurisation willnormally be less than 5% by wt. of the feedstock, but it may bedesirable to cool the reactor in which the desulphurisation reactiontakes place. This may be done by using recycle of elfluent to thereactor inlet or a cooled tubular reactor. The former is preferred,since it allows additional catalyst capacity to be convenientlyprovided, and is cheaper in capital cost than a tubular reactor. Thereaction may be carried out in liquid or gas phase, and in one or morereactors, provided that if more than one reactor is used, reactionconditions in each are identical.

The desulphurised product of the present process may be hydrogenatedover a suitable catalyst, such as a nickel or platinum hydrogenationcatalyst. A process for the hydrogenation of benzene containing lessthan 1 p.p.m. sulphur to cyclohexane using two hydrogenation stages isdisclosed in British patent application No. 28,767/65. The presentdesulphurisation process may be used to obtain benzene having less thanthe above amount of sulphur, and the hydrogenation process of thiscopending application preferably uses nickel on sepiolite as thecatalyst in each stage.

The invention is illustrated by the following example.

EXAMPLE Benzene containing 1.3 p.p.m. weight of sulphur wasdesulphurised over nickel on sepiolite catalyst under the followingconditions:

Pressure, p.s.i.g 3 Temperature, F 150 Space velocity, v./v./h 1.0 Inletgas Hydrogen Inlet H zhydrocarbon ratio, molar 0121 Under theseconditions 5 percent weight of benzene was converted to cyclohexane, andthe sulphur content of the product was 0.6 p.p.m. weight. However, theextent of the hydrogenation gradually decreased and the sulphur contentof the product increased. Consequently, the temperature was raised toimprove the desulphurisation efficiency. The effect of the changes inoperating temperature was as follows.

Cyclohexane Sulphur content; of content of Catalyst, Temperature,product, product, sulphur-nickel F percent wt. p.p.m. wt. ratio, atomicAt this point the plant pressure was raised to 15 p.s.i.g. and thelevels of hydrogenation and desulphurisation also increased.

836.--" 7.6 0.4 1, 420- 300 4. 2 0. 5 0f005i 1, 920- a. 5 0.8 0. 0072 Asthe activity of the catalyst declined further the temperature was againraised, and it was also possible to increase the pressure to 45 p.s.i.g.

0 has desulphurisation activity but less than 5% by weight of the feedis hydrogenated and no substantial amount of hydrogen sulphide isproduced, and progressively increasing the temperature within the saidrange as the catalyst takes up sulphur.

2. A process as claimed in claim 1, in which the feedstock is selectedfrom the group consisting of benzene and a major proportion of benzenein admixture with a minor proportion of material, other thansulphur-containing material, which is not substantially hydrogenatedunder the reaction conditions of temperature and pressure and which doesnot de-activate the catalyst surface under those conditions.

3. A process as claimed in claim 1 in which the supported nickelcatalyst is nickel on sepiolite.

4. A process as claimed in claim 3, in which the catalyst contains from1 to 50% wt. nickel expressed as elemental nickel, by weight of totalcatalyst.

5. A process as claimed in claim 1 in which the reaction temperature isincreased within the range 75 to 250 C.

6. A process as claimed in claim 1, in which the pressure is from O to50 p.s.i.g. when the catalyst sulphur: nickel atomic ratio is not morethan 0.121 and from 50 to 2000 p.s.i.g. when the sulphurznickel atomicratio is greater than 0.1:].

7. A process as claimed in claim 1, in which the space velocity is from0.05 to 10 v./v./hr., and the inlet hydrogenchydrocarbon mole ratio ontotal feed is 0.01 to 05:1.

8. A process as claimed in claim 1, in which contacting of the feedstockis carried out in the presence of a mixed gas containing hydrogen andone or more reactioninert constituents.

9. A process as claimed in claim 8, in which the mixed gas is a gascontaining approximately 95% hydrogen, together with methane.

10. A process as claimed in claim 3, in which the catalyst contains from5 to 25% Wt. nickel by weight of total catalyst.

11. A process as claimed in claim 1, in which the space velocity is from0.2 to 5.0 v./v./hr., and the inlet hydrogenzhydrocarbon ratio on totalfeed is 0.05 to 0.2: 1.

References Cited UNITED STATES PATENTS 1,897,798 2/1933 Guthke et al260674 2,587,987 3/1952 Franklin 19628 3,004,914 10/1961 White et al.208255 HERBERT LEVINE, Primary Examiner J. M. NELSON, Assistant ExaminerUS. Cl. X.R.

. (233? UNITED STATES PATENT OFFICE 1799) CERTIFICATE OF CORRECTIONPatent No. 3,484,367 Dated December 16, 1969 Inventor) John Winsor It iscertified that error appears in the above-identified patent: and thatsaid Letters Patent are hereby corrected as shown below:

Col. 1, line 33 for "it" read --is--;

Col. 1, line 43 for "nylon" read --Ny1on--;

C01. 3, line 34 for "0.053z1" read --0.53:1--;

C01. 3, line 37 for "00.51zl" read --0.045:1--;

Col. 3, line 69 for hydrogenations" read --hydrogenation--;

Col. 4, line 44, column headed "Temperatu gt for read --150--.

Sl'GNED AND SEALED JUL 1 4 1970 (S Attest:

Eawuaummh ,J. v

A er r WILLIAM E. mm. a ue u ()ffi Gomissioner of Patent:

